1. Field of the Invention
The invention relates to an inkjet recording apparatus in which an ink droplet is ejected from each of nozzles onto a recording medium.
2. Description of Related Art
As this kind of inkjet recording apparatus, there is known an apparatus where an actuator unit, such as an electromechanical transducer, e.g., a piezoelectric element, and an electrothermal transducer, is driven to vary the pressure in a pressure chamber in communication with one of nozzles so as to eject ink in the pressure chamber through the nozzle onto a recording medium, thereby performing printing.
Conventional inkjet recording apparatuses of this kind are classified into two groups based on the relative size difference between the actuator unit and the recording medium. Namely, a fixed-head type in which the recording medium is moved relatively to the actuator unit when printing is performed, and a serial type in which the actuator unit is also moved relatively to the recording medium when printing is performed. FIG. 8 presents a part of an inkjet recording apparatus of the latter type as disclosed in JP-A-2003-80793 corresponding to U.S. patent application Publication No. 2003063449A1 where a head holder holding a recording head 80 is mounted on a carriage. In FIG. 8 is presented a positional relationship between the head 80 on the head holder and an IC chip 84, as seen from the side of a nozzle surface 81 in which a plurality of nozzles are formed.
More specifically, the head 80 has the nozzle surface 81 in which the nozzles are open. The head 80 is generally rectangular and the nozzles are arranged in a plurality of rows or groups each extending along a longitudinal direction of the head 80. The number of the nozzle rows corresponds to the number of inks of respective colors used, and the nozzle rows are aligned in a width direction of the head 80 which is perpendicular to the longitudinal direction. In the head 80, there are formed ink supply ports 86a-86d at a position corresponding to ends of the respective nozzle rows on a same side in the direction of extension of each nozzle row. There is formed an ink supply passage which extends from an ink cartridge mounted on an upper, open side of the head holder, to the ink supply ports 86a-86d of the head 80, and includes an ink supply channel formed through the head holder.
At the side of the ones of the opposite ends of the respective nozzle rows which are remote from the ink supply ports 86a-86d, there is disposed an IC chip 84 having a drive circuit for outputting drive signals for driving an actuator unit disposed on a surface of the head opposite to the nozzle surface.
The IC chip 84 is long and disposed along the width direction of the head 80. On an upper surface of the IC chip 84, a heatsink 83 for releasing heat generated at the IC chip 84 is disposed. The heatsink 83 has a horizontally long, planar shape whose plane surface has an area larger than that of the upper surface of the IC chip 84, and is fixed to a wall surface of the head holder which is on a side opposite the ink supply ports of the head 80.
An ink ejection performance, including the speed at which ink droplets are ejected, varies with the viscosity of the ink, which in turn varies with the temperature of the ink. That is, a change in the ink temperature leads to a change in the ink ejection performance.
However, in the conventional inkjet recording apparatus as shown in FIG. 8, the heatsink 83 is disposed positionally correspondingly to the ends of the respective nozzle rows on the side remote from the ink supply ports 86a-86d. Hence, the temperature of the head body 80 is the highest at an area corresponding to the ends of the nozzle rows remote from the ink supply ports 86a-86d, and gradually decreases toward the ink supply ports 86a-86d. Since the temperature is decreased around the ink supply ports 86a-86d by the unwarmed ink flowing through the ink supply ports 86a-86d, the temperature at this place is further lowered.
Accordingly, in the nozzle surface 81, a variation in the temperature of the ink may occur, leading to a variation in the ink ejecting performance among nozzles depending upon their positions, namely, whether near the ink supply ports or the IC chip 84. This can cause deterioration in the quality of an image formed on the recording medium.
In particular, there has been recently a growing demand for an inkjet recording apparatus assuring a further enhanced recording quality and higher recording rate, resulting in the existing tendency of increasing the number of nozzles and shortening the interval of applications of the drive signals. This considerably raises the temperature of the IC chip 84, and an adverse influence of this rise in temperature on the recording quality has now become a matter of concern.